A typical technique for identifying stenotic regions in a blood vessel is using angiography, whereas the functional impact of the stenosis is quantified with the fractional flow reserve (FFR) technique. FFR is calculated from the ratio of pressures at the distal and proximal ends of the stenosis, measured with a sensor positioned at the tip of a wire. The FFR value is a measure of the severity of the stenosis, and it can be established whether the stenosis limits blood flow within the vessel to an extent that treatment is required. Common treatment options include angioplasty, stenting or bypass.
Angiography, a fluoroscopy imaging technique in conjunction with radio-opaque contrast agents, can be used to visualize the vasculature of a patient. Due to the nature of the technique, only the flow of the contrast agent can be imaged with fluoroscopy, therefore the cross-sectional shape of the lumen remains unknown, since the vessel wall and the surrounding tissue are not imaged. The weakness of the technique is that the cross-sectional shape of the stenosis can only be roughly estimated even by using multiple projections. Furthermore, such a visual evaluation of the stenotic region may be obstructed by other vessels that overlap the stenosis in the image, as well as by image artefacts and noise.
US 2015/0119705 A1 describes a method for evaluating a vessel of a patient based on obtaining physiology measurements from a first instrument and a second instrument positioned within the vessel of the patient while the second instrument is moved longitudinally through the vessel from a first position to a second position and the first instrument remains stationary within the vessel. The physiological measurements are based on local blood pressure measurements and the derived values such as FFR are presented on an angiographic image of the vessel. The output image is a visualization of vessels colorized according to the changes in pressure along the vessels, or a visualization of vessels by using a heat map representing FFR values.